As is known, high-speed rotation of the revolving drum of the washing machine produces severe machine vibrations which are transferred to the casing of the washing machine, and which normally become much more problematic as the speed of the revolving drums increases.
To reduce machine vibrations, in today's laundry washing machines the revolving drums is connected in floating manner to the casing by a suspension system designed to partially absorb vibrations before they reach the casing.
In particular installation conditions, however, the floating suspension system fails to sufficiently reduce machine vibrations reaching the casing, so that the washing machine becomes noisy. For example, when a washing machine rests on a flexible floor, such as a wooden floor, a soft floor, or a floor resting on a thin slab, the vibrations generated by the revolving drum during the spin cycle may be resonance-amplified to an unacceptable noise level, and may damage not only the washing machine but also the floor.
To overcame this drawback today's high-end washing machines are also provided with a vibration damper fixed to the casing to reduce vibrations of the washing machine at resonance speeds, and which comprises an oscillating mass and a number of coil springs connecting the oscillating mass to the washing machine casing. The oscillating mass and the coil spring system are properly dimensioned to vibrate, during rotation of the drum, out of phase with respect to vibrations transmitted by the floating suspension system of the drum, thus reducing the amplitude of the casing vibrations.
Unfortunately currently used vibration dampers (traditionally known as “Frahm dampers”) only provide for optimum damping performance over a limited range of the possible drum rotation speeds.